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Chowdhury S, Crocker NA, Peebles WA, Rhodes TL, Zeng L, Lantsov R, Van Compernolle B, Brookman M, Pinsker RI, Lau C. A novel Doppler backscattering (DBS) system to simultaneously measure radio frequency plasma fluctuations and low frequency turbulence. Rev Sci Instrum 2023; 94:073504. [PMID: 37493501 DOI: 10.1063/5.0149654] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Subscribe] [Scholar Register] [Received: 03/07/2023] [Accepted: 07/12/2023] [Indexed: 07/27/2023]
Abstract
A novel quadrature Doppler Backscattering (DBS) system has been developed and optimized for the E-band (60-90 GHz) frequency range using either O-mode or X-mode polarization in DIII-D plasmas. In general, DBS measures the amplitude of density fluctuations and their velocity in the lab frame. The system can simultaneously monitor both low-frequency turbulence (f < 10 MHz) and radiofrequency plasma density fluctuations over a selectable frequency range (20-500 MHz). Detection of high-frequency fluctuations has been demonstrated for low harmonics of the ion cyclotron frequency (e.g., 2fci ∼ 23 MHz) and externally driven high-frequency helicon waves (f = 476 MHz) using an adjustable frequency down conversion system. Importantly, this extends the application of DBS to a high-frequency spectral domain while maintaining important turbulence and flow measurement capabilities. This unique system has low phase noise, good temporal resolution (sub-millisecond), and excellent wavenumber coverage (kθ ∼ 1-20 cm-1 and kr ≲ 30 cm-1). As a demonstration, localized internal DIII-D plasma measurements are presented from turbulence (f ≤ 5 MHz), Alfvenic waves (f ∼ 6.5 MHz), ion cyclotron waves (f ≥ 20 MHz), as well as fluctuations around 476 MHz driven by an external high-power 476 MHz helicon wave antenna. In the future, helicon measurements will be used to validate GENRAY and AORSA modeling tools for prediction of helicon wave propagation, absorption, and current drive location for the newly installed helicon current drive system on DIII-D.
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Affiliation(s)
- S Chowdhury
- Physics and Astronomy Department, University of California Los Angeles, Los Angeles, California 90098, USA
| | - N A Crocker
- Physics and Astronomy Department, University of California Los Angeles, Los Angeles, California 90098, USA
| | - W A Peebles
- Physics and Astronomy Department, University of California Los Angeles, Los Angeles, California 90098, USA
| | - T L Rhodes
- Physics and Astronomy Department, University of California Los Angeles, Los Angeles, California 90098, USA
| | - L Zeng
- Physics and Astronomy Department, University of California Los Angeles, Los Angeles, California 90098, USA
| | - R Lantsov
- Physics and Astronomy Department, University of California Los Angeles, Los Angeles, California 90098, USA
| | - B Van Compernolle
- General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
| | - M Brookman
- General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
| | - R I Pinsker
- General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
| | - C Lau
- Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA
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